To provide the transmission line changeover method by which a spare transmission line is surely selected on the occurrence of a fault.
An active line and a standby line are assigned to the user by an operation center with respect to an application from the user, and the result is reported of a test start station. When there is a band to be assigned (S2), the test start station uses a switching cell to make an assignment test instruction to a terminal station via a relay station (S3). When the relay station receives a switching cell (S11), the relay station discriminates the presence of the band to be assigned (S12), and sends the switching cell toward a terminal station when in existence (S14). Upon the receipt of the switching cell (S21), the terminal station discriminates the presence of the band to be assigned (S22) and sets a standby line when in existence (S23), and makes a normal end reply to the test start station (S24). The test start station receives the reply from the terminal station (S4) and sets the standby line when normal (S6).
MIYAZAKI TATSUTOSHI
MASUDA SHIGETO
YAMAMICHI NOBORU
OKI ELECTRIC IND CO LTD
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